1. Field of the Invention
This invention relates to air-actuated diaphragm spring brakes having a push rod actuator. More particularly, this invention relates to an apparatus which alerts observers that the brakes are seriously worn or not functioning properly, such indication remaining active irrespective of subsequent positioning of the push rod.
2. State of the Prior Art
Air brake systems which provide an indication to the operator of excess wear or misadjustment of vehicle brakes have previously been described. See for example U.S. Pat. No. 4,855,712 issued Aug. 9, 1989 to Wiley Jr. et al. and U.S. Pat. No. 4,945,818 issued Aug. 7, 1990 to Ware.
The Wiley Jr. et al. patent discloses the use of a magnetic system having a magnet attached to the brake push rod which moves with that push rod. A detector, which detects movement of the magnet, is placed in a fixed position with respect to the push rod. When an indication is received that the magnet, and hence the brake push rod, have moved beyond a pre-determined point, a visual or audible indicator is actuated in the truck cab to signal the operator of a brake problem. Movement of the brake push rod beyond a pre-determined point is an indication that the brakes have worn beyond a safe level, or that the brakes have been misaligned or are misadjusted in some manner, or that complete brake failure has occurred.
The Ware patent discloses the use of a physical indicia cut into the push rod at a pre-determined area of the push rod. This area will be exposed to the operator's view if the push rod is extended beyond a pre-determined point. Again, this provides an indication to the operator of a brake problem.
None of these prior art patents provide for the fixing of the break wear indication signal so that the signal remains on, once the push rod has moved beyond a pre-determined point, irrespective of subsequent positioning of the brake push rod. These prior art monitoring devices all have the disadvantage of switching off when the push rod is retracted after pressure is released from the brake, and there is no permanent indication that a dangerous brake situation has occurred.
There is a need for an apparatus to monitor brakes which will remain fixed in position, and thereby provide a constant signal, when the push rod has moved beyond a pre-determined position, thereby providing a permanent indication of excessive brake wear, misalignment or brake failure, irrespective of the subsequent positioning of the push rod.